System and method for information verification based on channel awareness

ABSTRACT

This disclosure describes techniques for operating a client device to communicate with a wireless access point to validate data within a frame by comparing channel quality metrics and duration metrics to thresholds. Information received within a validity window may be treated as correctly received even if the frame fails a subsequent verification process or if reception of the frame is terminated prior to the end of the frame.

RELATED APPLICATIONS

The present application claims priority of pending provisional patentapplication Ser. No. 61/595,562 filed Feb. 6, 2012.

FIELD OF THE PRESENT INVENTION

This disclosure relates generally to wireless networking. Morespecifically, this disclosure relates to techniques for validatinginformation received in a transmitted frame prior to receiving the endof the frame.

BACKGROUND OF THE INVENTION

A wireless network may comprise an access point and at least one clientdevice. The access point may be coupled to a network, such as theInternet, and enable the client device to communicate via the network(and/or communicate with other devices coupled to the access point).Generally, the wireless access point may send data to the at least oneclient device in the form of one or more frames. To reduce powerconsumption, a client device may operate in a low power consumption mode(e.g., a sleep mode) in some circumstances, such as when the clientdevice is not being used for communications (e.g., with the accesspoint). Under the IEEE 802.11 X (e.g., 802.11b, 802.11g, 802.11n)standards for WI-FI communications, a client device may periodicallyawake from a low power consumption mode, and receive a beacon from anaccess point. The beacon may include information regarding present orfuture communications between the client device and the access point.According to one example, the beacon may include information such as atraffic indication map (TIM) and/or a delivery traffic identificationmessage (DTIM) information elements (IE) that indicates whether framesof data are waiting to be communicated to the client device. Further,the beacon may also contain other information pertinent to the operationof the network, delivered as an IE or in other suitable manners.

To provide further power saving advantages, techniques have beendeveloped to maximize time spent in low power mode, allowing the deviceto return to a low power mode of operation before an entire beacon isreceived by the client device. For example, a client device may awakefrom a low power mode of operation to receive a first portion of abeacon. As discussed above, a portion of the beacon may includeinformation related to communications with the access point, such as anindication of whether one or more frames of data are forthcoming fromthe access point (e.g., waiting to be sent to the client device). Insome embodiments, this information is contained in the DTIM. If theinformation from the access point indicates no frames of data areforthcoming, the client device preferably returns to a low powerconsumption mode of operation before receiving subsequent portions ofthe beacon. As will be appreciated, such techniques allow the clientdevice to spend a greater portion of time in low power mode, reducingthe overall power consumption associated with access pointcommunications. Such strategies are generally referred to herein asearly beacon termination (EBT) techniques and are known in the art.

Despite the power saving advantages represented by EBT techniques, itwould be desirable to optimize certain performance aspects. Typically,wireless communication devices are designed so that important systemparameters will not be updated on the basis of a received frame unlessthe integrity of that frame can be confirmed. One example is the timesynchronization function (TSF) used to keep the clocks on the clientdevice and the access point coordinated. Since synchronization iscritical to proper functioning, the client device will not update itsTSF unless there is reasonable confidence in the validity of the timinginformation transmitted by the access point. However if the clientdevice is not able to validate the TSF for a sufficient period of time,clock drift that affects each device may result in the client devicebeing out of synchronization with the access point, impairingperformance. Another important system parameter relates to coordinatedchannel switching involving the access point and a client device. Theaccess point may indicate an imminent switch to a different channel,such as to avoid interference, using the channel switch announcement(CSA) IE. Since transmission will be interrupted if the client deviceswitches channels erroneously, it is generally desirable to have a highdegree of confidence in the validity of the CSA IE before implementing aswitch.

Positioning of the DTIM within the beacon may not be mandated by thewireless specifications, but often occurs relatively early and beforevalidation information which typically comes towards the end oftransmissions. In the IEEE 802.11X protocols, for example, frames endwith a frame check sequence (FCS) IE that allows the client device toverify the integrity of the received frame. Similarly, other networkinformation may also be contained in the beacon and positioned atvarious point relative to the FCS. Accordingly, when a period timeelapses during which the access point has no frames to transmit to theclient device, EBT will result in the client device returning to lowpower mode before the FCS. In turn, information transmitted by theaccess point cannot be verified and parameters such as TSF and CSA maynot be updated. System parameters relying on other network informationmay be similarly affected.

Another aspect of the impact of EBT strategies results from thearchitecture of the beacon frame. As noted earlier, IEEE 802.11Xprotocols generally result in the DTIM occurring relatively early in thebeacon frame. This is followed by a variable number of additional IEsand finally by the FCS. As a practical matter, channel conditions changeconstantly in a typical wireless communication system. Thus, there aresituations in which the channel is good enough for valid receptionduring the DTIM, but the quality will erode over the successive IEs andultimately fail the FCS. This may occur when the time between the DTIMand the FCS exceeds the coherence time of the channel or if there is adeep fade in the signal during the period. While the former may beequalized to some extent by efficient pilot interpolation, which isoptionally applied due to varying degrees of implementationcomplexities, the latter would certainly result in irrecoverable errorsand lead to FCS failures. Under prior EBT mechanisms, the client devicesimply discards the frame even though the DTIM was set because thechannel has degraded to the point that the FCS fails, even though theDTIM or other network information may have been received while thechannel was still valid. Correspondingly, under such situations, theperformance of the client device will suffer since it is disregardingvalid data, such as missing the opportunity to respond to the accesspoint with a power save poll (PS-POLL) to enable the access point todeliver waiting frames to the client device or failing to updateimportant system parameters.

Accordingly, it would be desirable to provide a wireless communicationsystem that features the power saving benefits represented by an EBTfunction while minimizing the impact on performance. To that end, itwould be desirable for a client device to be able to update importantsystem parameters even when the client device is not receiving a beacontransmission in its entirety. It would also be desirable to provide sucha wireless communication system that can utilize a valid DTIM or otherIE even when the channel degrades over time and causes the FCS to fail.This disclosure is directed to systems and methods that accomplish theseand other goals.

SUMMARY OF THE INVENTION

In accordance with the above needs and those that will be mentioned andwill become apparent below, this disclosure is directed to a clientdevice for communicating with a wireless access point, wherein theclient device includes a data processing module configured to receive atleast a portion of a frame transmitted by the access point to anintermediate location within the frame and a channel assessment moduleconfigured to determine a validity window with respect to theintermediate location when at least one channel quality metric isgreater than or equal to a given threshold, wherein data processingmodule is configured to validate information received within thevalidity window.

In one aspect, wherein the channel assessment module may be configuredto determine the validity window by setting a range of symbols upstreamand downstream of a period of time when the channel quality metric isdetermined. Further, the channel quality metric may be confidencemetrics from the output of a Viterbi decoder.

In another aspect, the channel assessment module may be configured todetermine the validity window based upon a coherence time for a channelused to transmit the frame. Additionally, the channel quality metric mayinclude a receiver error vector magnitude. The channel quality metricmay also be based upon signal strength of the frame. Further, the giventhreshold may be based upon the modulation coding set used for thetransmitted frame.

In some embodiments, the client device may be configured to updatesystem parameters based upon the information received within thevalidity window. As desired, the client device may be configured toterminate reception of the frame when the channel quality metric doesnot exceed the given threshold.

Another aspect of the disclosure relates to channel assessment modulebeing configured to determine a plurality of validity windows, such thateach validity window is determined in reference to a channel qualitymetric determined at a different time during the frame.

Some embodiments include receiving the frame though a verification fieldsuch that the channel assessment module may be configured to diagnose afailure of the verification field on the basis of a duration metric anda difference between a first channel quality metric measured during apreamble of the frame and a second channel quality metric measuredduring a time corresponding to the intermediate location, wherein theinformation within the validity window is validated when the failurediagnosis is attributable to deteriorating channel conditions.

In yet another aspect, when the information received within the validitywindow is a DTIM information element, the client device may beconfigured to terminate reception of the frame and enter a low powermode if the DTIM information element indicates there is no pending dataat the access point for the client device.

In some embodiments, the channel assessment module may be furtherconfigured to assign a confidence level to the validity window basedupon the channel quality metric and the given threshold.

Further, the channel assessment module may be configured to determinethe validity window by comparing a first duration metric correspondingto a time period between a preamble of the frame and the intermediatelocation to a coherence time and determining whether a channel qualitymetric determined from the preamble exceeds a given threshold. In suchembodiments, the channel assessment module may also determine thevalidity window by comparing a second duration metric corresponding to atime period between the intermediate location and a verification fieldto a coherence time and comparing the difference between the firstchannel quality metric and a second channel quality metric to a channelquality difference threshold.

This disclosure is also directed to a method for wireless communicationwith an access point, including the steps of receiving at least aportion of a frame transmitted by the access point to an intermediatelocation within the frame with a client device, determining a channelquality metric, establishing a validity window when the channel qualitymetric is greater than or equal to a given threshold, and validatinginformation from the frame received within the validity window.

In one aspect, establishing the validity window may include setting arange of symbols upstream and downstream of a period of time when thechannel quality metric is determined.

Further, determining the channel quality metric may include obtainingconfidence metrics from the output of a Viterbi decoder. Additionally,establishing the validity window may include using a range based upon acoherence time for a channel used to transmit the frame.

In some embodiments, determining the channel quality metric may includemeasuring a receiver error vector magnitude. Determining the channelquality metric may also include measuring a signal strength of theframe.

Additionally, the given threshold may be based upon the modulationcoding set used for the transmitted frame.

The method may also include updating system parameters of the clientdevice based upon the information received within the validity window.As desired, the method may include terminating reception of the framewhen the channel quality metric does not exceed the given threshold.

Yet another aspect may include determining a plurality of channelquality metrics at different times during the frame and establishing aplurality of validity windows, each validity window corresponding to theplurality of channel quality metrics.

When the frame is received though a verification field, the method mayinclude diagnosing a failure of the verification field on the basis of aduration metric and a difference between a first channel quality metricmeasured during a preamble of the frame and a second channel qualitymetric measured during a time corresponding to the intermediatelocation, wherein the information within the validity window isvalidated when the failure diagnosis is attributable to deterioratingchannel conditions.

Further, when the validated information includes a DTIM informationelement, the method may also include terminating reception of the frameand placing the client device in a low power mode if the DTIMinformation element indicates there is no pending data at the accesspoint for the client device.

In one embodiment, the method may also include assigning a confidencelevel to the validity window based upon the channel quality metric andthe given threshold.

In some embodiments, establishing the validity window may includecomparing a first duration metric corresponding to a time period betweena preamble of the frame and the intermediate location to a coherencetime and determining whether a channel quality metric determined fromthe preamble exceeds a given threshold. Establishing the validity windowmay further include comparing a second duration metric corresponding toa time period between the intermediate location and a verification fieldto a coherence time and comparing the difference between the firstchannel quality metric and a second channel quality metric to a channelquality difference threshold.

The details of one or more examples of this disclosure are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the techniques described herein will beapparent from the description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages will become apparent from the followingand more particular description of the preferred embodiments of theinvention, as illustrated in the accompanying drawings, and in whichlike referenced characters generally refer to the same parts or elementsthroughout the views, and in which:

FIG. 1 is a conceptual diagram that illustrates one example of an accesspoint configured to generate a wireless network that may be usedaccording to the invention;

FIG. 2 is a conceptual diagram that illustrates one example of a framethat may be communicated by an access point to a client device;

FIG. 3 is a block diagram that illustrates one example of an accesspoint and a client device configured to operate according to oneembodiment of the invention;

FIG. 4 is a flow diagram that illustrates one example of a method ofoperating a client device to receive a beacon, according to oneembodiment of the invention;

FIG. 5 is a flow diagram that illustrates another example of a method ofoperating a client device to receive a beacon, according to oneembodiment of the invention;

FIG. 6 is a flow diagram that illustrates an example of a method ofoperating a client device to receive a frame, according to oneembodiment of the invention;

FIGS. 7-10 depict experimental results using a signal to noise ratiobased channel quality metric, according to embodiments of the invention;and

FIGS. 11 and 12 depict experimental results using a Viterbi output basedchannel quality metric, according to embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

At the outset, it is to be understood that this disclosure is notlimited to particularly exemplified materials, architectures, routines,methods or structures as such may, of course, vary. Thus, although anumber of such options, similar or equivalent to those described herein,can be used in the practice or embodiments of this disclosure, thepreferred materials and methods are described herein.

It is also to be understood that the terminology used herein is for thepurpose of describing particular embodiments of this disclosure only andis not intended to be limiting.

Some portions of the detailed descriptions which follow are presented interms of procedures, logic blocks, processing and other symbolicrepresentations of operations on data bits within a computer memory.These descriptions and representations are the means used by thoseskilled in the data processing arts to most effectively convey thesubstance of their work to others skilled in the art. In the presentapplication, a procedure, logic block, process, or the like, isconceived to be a self-consistent sequence of steps or instructionsleading to a desired result. The steps are those requiring physicalmanipulations of physical quantities. Usually, although not necessarily,these quantities take the form of electrical or magnetic signals capableof being stored, transferred, combined, compared, and otherwisemanipulated in a computer system.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. Unlessspecifically stated otherwise as apparent from the followingdiscussions, it is appreciated that throughout the present application,discussions utilizing the terms such as “accessing,” “receiving,”“sending,” “using,” “selecting,” “determining,” “normalizing,”“multiplying,” “averaging,” “monitoring,” “comparing,” “applying,”“updating,” “measuring,” “deriving” or the like, may refer to theactions and processes of a computer system, or similar electroniccomputing device, that manipulates and transforms data represented asphysical (electronic) quantities within the computer system's registersand memories into other data similarly represented as physicalquantities within the computer system memories or registers or othersuch information storage, transmission or display devices.

As such, techniques described herein may be implemented in hardware,software, firmware, or any combination thereof, unless specificallydescribed as being implemented in a specific manner. Any featuresdescribed as modules or components may also be implemented together inan integrated logic device or separately as discrete but interoperablelogic devices. If implemented in software, the techniques may berealized at least in part by a tangible processor-readable storagemedium comprising instructions that, when executed, performs one or moreof the methods described above. The tangible processor-readable datastorage medium may form part of a computer program product, which mayinclude packaging materials. Accordingly, embodiments described hereinmay be discussed in the general context of processor-executableinstructions residing on some form of processor-readable medium, such asprogram modules, executed by one or more computers or other devices.Generally, program modules include routines, programs, objects,components, data structures, etc., that perform particular tasks orimplement particular abstract data types. The functionality of theprogram modules may be combined or distributed as desired in variousembodiments.

By way of example, and not limitation, the tangible processor-readablestorage medium may comprise random access memory (RAM) such assynchronous dynamic random access memory (SDRAM), read only memory(ROM), non-volatile random access memory (NVRAM), electrically erasableprogrammable read-only memory (EEPROM), FLASH memory, magnetic oroptical data storage media, and the like. The techniques additionally,or alternatively, may be realized at least in part by aprocessor-readable communication medium that carries or communicatescode in the form of instructions or data structures and that can beaccessed, read, and/or executed by a computer.

The instructions may be executed by one or more processors, such as oneor more digital signal processors (DSPs), general purposemicroprocessors, application specific integrated circuits (ASICs),application specific instruction set processors (ASIPs), fieldprogrammable gate arrays (FPGAs), or other equivalent integrated ordiscrete logic circuitry. The term “processor,” as used herein may referto any of the foregoing structure or any other structure suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated software modules or hardware modules configured as describedherein. Also, the techniques could be fully implemented in one or morecircuits or logic elements.

In the figures, a single block may be described as performing a functionor functions; however, in actual practice, the function or functionsperformed by that block may be performed in a single component or acrossmultiple components, and/or may be performed using hardware, usingsoftware, or using a combination of hardware and software. Also, theexemplary radio modules, RF components, and end products may includecomponents other than those shown, including well-known components suchas a processor, memory and the like.

For purposes of convenience and clarity only, directional terms, such astop, bottom, left, right, up, down, over, above, below, beneath, rear,back, and front, may be used with respect to the accompanying drawingsor particular embodiments. These and similar directional terms shouldnot be construed to limit the scope of the invention in any manner andmay change depending upon context. Further, sequential terms such asfirst and second may be used to distinguish similar elements, but may beused in other orders or may change also depending upon context.

As used herein, the term “DTIM” refers to both the delivery trafficindication message as well as the traffic indication message (TIM) IEsdefined by IEEE 802.11 protocols. Generally, when the DTIM is set, theaccess point is indicating that broadcast data is ready to betransmitted and the client device prepare to receive data frames.Likewise, when TIM is set, the access point is indicating that dataspecific to the client device is ready to be transmitted and the clientdevice responds that it is ready to receive that data by sending aPS-POLL message. However, the techniques of this disclosure areapplicable to any other suitable wireless communication system.Accordingly, this term is also used herein to refer to any portion of abeacon transmission containing information about data waiting to be sentto a client device.

Further, embodiments are discussed in specific reference to wirelessnetworks. As such, this disclosure is applicable to any suitablewireless network having the necessary characteristics, includingwireless local area networks (WLAN), particularly those governed by IEEE802.11 protocols, as well as wireless fidelity (WiFi), Wibree™, ultrawideband (UWB), Long Term Evolution (LTE), Enhanced Data for GSMEvolution (EDGE), Evolution Data Optimized (EVDO), General Frame RadioService (GPRS) networks and others.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one having ordinaryskill in the art to which the disclosure pertains.

Further, all publications, patents and patent applications cited herein,whether supra or infra, are hereby incorporated by reference in theirentirety.

Finally, as used in this specification and the appended claims, thesingular forms “a, “an” and “the” include plural referents unless thecontent clearly dictates otherwise.

Aspects of this disclosure discussed herein are directed to improvingthe performance of a wireless communication system by assessing channelconditions at a receiving device and using a series of channel awarenessparameters, including a channel quality metric (CQM), in order to definea validity window during which received information may be treated ascorrect even if reception of the frame is terminated prematurely or ifthe frame fails conventional verification. Suitable information that mayform the basis for determining a CQM include one or more measurementsassociated with the channel, including signal strength measurements suchas signal to noise ratio (SNR), signal plus interference to noise ratio(SINR), and received signal strength indicator (RSSI), which preferablyare obtained directly from the physical layer (PHY) of the devicereceiving the frame. In one aspect, the preamble of an IEEE 801.11 Xframe contains the necessary Short Training Field (STF) and LongTraining Field (LTF) signals to compute the CQM. Further, the CQM mayinclude confidence metrics from the Viterbi decoder output. Yet anothersuitable CQM may be the Receiver Error Vector Magnitude (Rx-EVM), asderived from the difference between the ideal and observed constellationpoints after symbol demodulation of the instantaneous pilots. Asdesired, these values may be used singly, as a composite or in someother combination. Also preferably, these measurements are available foreach antenna or in multiple input systems having receive diversity, theCQM may be a maximal ratio combined (MRC) composite, or other suitablecombination. In some aspects, the characteristic used for the CQM may beupdated more frequently. For example, the SNR metric may be determinedin prior art devices only at the end of the frame. However, it may bedesirable to determine the SNR after every symbol or at definedintervals.

FIG. 1 is a conceptual diagram that illustrates one example of awireless access point 101. Generally speaking, access point 101 maycomprise one or more devices operative to generate a wireless local areanetwork (WLAN) to communicatively couple one or more of client devices103A-103F with one or more other computing devices (not shown in FIG. 1)via a larger, non-local network, such as a wide area network (WAN), orsuch as Internet 106, which is sometimes referred to as a globalcomputer network. According to the non-limiting example of FIG. 1,access point 101 is configured to generate a local wireless network forone or more of a desktop computer 103A, a mobile phone 103B, a printer103C, a smart phone or tablet computing device 103D, a televisiondisplay 103E, and a laptop computer 103F. Access point 101 may also orinstead operate to enable many other types of devices not specificallyshown in FIG. 1 to communicate with one another via the local wirelessnetwork and/or Internet 106, and/or with other devices via Internet 106.For example, client devices 103A-103F may include any device thatincludes a communications module configured to enable the respectiveclient device to wirelessly communicate with access point 101. Accordingto one such example, where access point 101 is configured to generate awireless local area network, such as an IEEE 802.11x, or so-called WI-FInetwork, wireless client devices 103A-103F may include any device with aWI-FI component (e.g., application specific integrated circuit (ASIC),field programmable gate array (FPGA), discrete logic and/or softwareexecutable by a processing device) configured to enable WI-FIcommunications with access point 101.

Access point 101 may use a wired or wireless communications protocol toestablish a communications link with Internet 106, and/or with a widearea network. For example, access point 101 may utilize one or more of acable modem, a digital service link (DSL) modem, an opticalcommunications link such as a T1 or T3 line, or any other form of wiredcommunications protocol to communicatively couple access point 101 toInternet 106. According to other examples, access point 101 may bewirelessly coupled to Internet 106. For example, access point 101 may bewirelessly coupled to Internet 106 via a cellular communications network(e.g., 3G, 4G), satellite communications network, or other form ofwireless communications that enables access point to communicate viaInternet 106.

In some examples, access point 101 may include a device specificallyconfigured to communicatively couple one or more client devices103A-103F to Internet 106, such as a wired (e.g., Ethernet) or wireless(e.g., WI-FI) router, or a cellular to WI-FI hotspot device. Accordingto other examples, access point 101 may comprise a more general purposecomputing device (e.g., such as one or more of client device 103A-103F)configurable to generate a local network. For example, access point 101may comprise a mobile phone or tablet computer configured to generate aWI-FI wireless network from a wireless cellular network connection. Insome examples, one or more devices 103A-103F may also further beconfigurable to operate as a client device, an access point, or bothsimultaneously, consistent with the techniques described herein.

In some examples, one or more of client devices 103A-103F maycommunicate with access point 101 via a wired or wired connection. Forexample, when a cable (e.g., an Ethernet cable, USB cable, or the like)is coupled between the respective client device 103A-103F and accesspoint 101, the client device may use a wired communications protocol(e.g., ETHERNET, UNIVERSAL SERIAL BUS (USB)) to communicate with accesspoint 101. However, when such a cable is not coupled between therespective client device 103A-103F and access point 101, the clientdevice may instead use a wireless network (e.g., WI-FI) to communicatewith access point 101.

In some examples, where access point 101 is configured to generate alocal wireless network, access point 101 may communicate with one ormore of client devices 103A-103F by sending data arranged into one ormore frames. For example, access point 101 may send to one or more ofclient device 103A-103F one or more frames of data received from anothercomputing device accessible via Internet 106, or from another of clientdevices 103A-103F. Access point 101 may also be configured to receiveone or more frames of data from one or more of client devices 103A-103F,and send the one or more received frames to another computing deviceaccessible via Internet 106, and/or another of the one or more clientdevices 103A-103F.

In some examples of wireless communication techniques, such as one ormore of the IEEE 802.11X (e.g., 802.11a, b, g or n) standards for WI-FIcommunications, some client devices 103A-103F may be configured tooperate in a low power consumption (sleep) mode, when the client deviceis not actively operating to communicate. According to such a low powermode, the client device 103A-103F may modify operation of one or morecomponents of the client device. For example, a client device 103A-103Foperating in such a low power consumption mode may turn off (e.g.,disconnect from a power supply) one or more components (e.g.,communications modules of the client device) that operate to enablecommunications with access point 101 or another device (e.g., one ormore other client devices 103A-103F). In other examples of such a lowpower consumption mode, the client device may also or instead modifyoperation of the client device by operating one or more components at alower voltage and/or lower operating power and/or speed than in anactive mode of operation.

In some examples, a client device 103A-103F may periodically awake froma low power mode, to receive a beacon from access point 101. Such abeacon may be provided by a wireless signal, and may include informationregarding further communications with the access point 101. As discussedabove, each beacon may include a plurality of IEs that may eachindicate, to or more of client devices 103A-103F, information regardingpresent or future communications with access point 101. For example, theplurality of IEs may indicate details regarding further communicationsbetween access point 101 and one or more of client devices 103A-103F,among other information.

In some examples, access point 101 may send one or more of clientdevices 103A-103F a beacon that includes an IE that comprises a DTIM.The DTIM may indicate whether access point 101 has one or more frames ofdata to communicate to the client device 103A-103F. As will be describedherein, client device 103A-103F preferably is configured to enter a lowpower mode upon determination of a valid DTIM indicating no data isforthcoming from access point 101.

According to some techniques for wireless communication (e.g., the IEEE802.11X WIFI standards), a client device may periodically awake fromsleep to receive a beacon from an access point, and remain in an activestate until all the data of the beacon (e.g., all IEs of the beacon)have been received and/or processed by the client device. Once all thedata has been received by the client device, the client device may thenverify the received data, such as by performing a FCS (for example,performing a cyclic redundancy check (CRC)) on the received beacon. Oncethe data of the beacon has been verified, the client device may use theverified data to operate the client device, such as by configuringsystem parameters of client device 103A-103F to facilitate furthercommunication with access point 101.

After receiving the entire beacon and performing the FCS check on dataof the beacon, the client device may return to the low power consumptionmode of operation described above, if no frames of data are forthcomingfrom the access point. However, if the DTIM message of the beaconindicates that there are frames of data forthcoming (e.g., waiting to besent to the client device) from the access point, the client device mayremain in an active mode (not return to a low power consumption mode)after receiving the beacon, to receive the forthcoming frames.

In some examples, a beacon may be relatively large (e.g., a relativelylarge number of bits of data). According to these examples, a clientdevice may remain in an active state for a significant amount of time toreceive and/or process a beacon. In some examples, periodically wakingto receive an entire beacon may cause an undesirable drain on powerresources of a client device. In some examples, power consumption of aclient device may be reduced by reducing the wake-up frequency at whichthe client device awakens from a low power consumption mode to receivebeacons from the access point. This approach, however, may cause areduction in the rate at which data is communicated, because thetransmission of frames from the access point may be delayed due to thereduced wake-up frequency of the client device.

Generally, wireless communication systems utilize management frames suchas a beacon to communicate the information necessary to configure theaccess point and client devices. Each management frame is composed of aseries of information elements (IEs) that correspond to various systemparameters and other network characteristics. As referenced above, someof the embodiments of the disclosure are discussed primarily with regardto general IEEE 802.11X protocols. In this context, FIG. 2 is aconceptual diagram that illustrates one example of a beacon frame 201adhering to IEEE 802.11X protocols. It should be recognized that thefollowing techniques are applicable to other IEEE 802.11X frames as wellas to other wireless systems that may use different architectures buthave analogous features.

Beacon 201 is sent by access point 101 and at least a portion may bereceived and/or processed by a client device 103A-103F according to thetechniques described herein. Generally speaking, beacon 201 may beperiodically transmitted by a wireless access point (e.g., access point101 depicted in FIG. 1) to a wireless client device (e.g., one or moreof client devices 103A-103F depicted in FIG. 1). The beacon may includeDTIM information regarding the further communication of data by wirelessaccess point 101 to client device 103A-103F, as well as otherinformation such as TSF, CSA and the like.

The exemplary beacon 201 comprises a sequence of transmittedinformation, initiating with physical layer convergence protocol (PLCP)preamble 202, starting at time T₀. In some embodiments, as will bediscussed below, an initial channel quality metric (CQM) may be measuredduring preamble 202, such as at T_(CQM1). Next is the physical layerservice data unit (PSDU) 203 frame which has three relevant transitionpoints. The start of the PSDU frame 203 occurs subsequent to T_(CQM1)with transmission of header 204, which may include information regardingone or more other components of beacon 201. For example, header 204 mayindicate what information is included in beacon 201, a location ofparticular information within beacon 201, a length of beacon 201, and/orother information. Header 204 is followed by a plurality of IEs 205directed to system parameters including the DTIM, TSF, CSA IEs andothers. As will be appreciated, the relative positions of the variousIEs may vary.

At a desired location within the body of beacon 201, an intermediate IEmay be identified to facilitate a determination of a CQM correspondingto the intermediate IE or other IEs. In the specific examples discussedbelow that are provide for illustration and not limitation, theintermediate IE may be DTIM IE 206 sent at time T_(TIM), as shown. Inother embodiments, other IEs may be used as desired. As noted above,DTIM IE 206 may indicate whether or not access point 101 has one or moreframes of data to send to client device 103A-103F. According to at leastsome aspects of this disclosure, client device 103A-103F may identifyDTIM IE 206 based on information of header 204 and/or header informationof DTIM IE 206, and process DTIM IE 206 to determine whether accesspoint 101 has any frames to send to the client device.

In some embodiments, an intermediate CQM may be measured at the time theintermediate IE is received to determine a validity window as describedbelow. Alternatively, the intermediate CQM may be measured at a timeoccurring before or after the intermediate IE is received. Preferably,when the intermediate CQM is measured at a time that is not coincidentwith the reception of the intermediate IE, it may be measured within thevalidity window during which it may be expected that the measure CQMwill apply to the time at which the IE is received. For example, thevalidity window may be established, at least in part, by the coherencetime (T_(C)) of the channel. Further, as will be appreciated, aplurality of intermediate CQMs may be measured at or near acorresponding plurality of intermediate IEs distributed throughoutbeacon 201.

DTIM IE 206, or another suitable intermediate IE, is succeeded byanother plurality of IEs 207 and beacon 201 is terminated by FCS 208 atT_(FCS). The techniques of this disclosure make reference to twoduration metrics associated with periods of time within beacon 201,measured in reference to DTIM IE 206, or another suitable intermediateIE. As shown, the first duration metric is the preamble to DTIMduration, Δ_(PT), and the second duration metric is the DTIM to FCSduration, Δ_(TF). The start of PSDU frame 203 occurs at T_(CQM1),representing the first portion of the transmission for which there isCQM information when an initial CQM is measured during the PLCP preamble202.

In some situations, there are a significant number of IEs 205 and 207,such as 40-60 or more. As a result, beacon 201 may require a significantperiod of time to transmit, during which channel conditions may change.When channel conditions deteriorate, they may reach a level at which thebeacon is subject to errors, such as burst symbol erasures and others,rendering the data from the rest of beacon 201 invalid and resulting inthe verification failure of FCS 208. This stage is indicated on FIG. 2by the time T_(CQM2), at which point a terminal CQM is determined.

In view of the specific time points discussed above, this disclosurerefers to three specific zones. T_(CQM1) marks the beginning of a firstcoherent zone, PTTh zone 210, corresponding to the time between theheader 204 and incorporating DTIM IE 206. Next is a second coherentzone, TFTh zone 211, beginning at T_(TIM) and running to T_(CQM2), apoint at which the channel assumptions of zone 210 are no longer valid.As will be appreciated, these zones are defined, at least in part, bythe T_(C) of the channel. Finally, an error zone 212 corresponds to theportion of beacon 201 in which the channel may have degraded, from thezone 210 and 211, to a degree that the information is not correctlydecoded. As can be seen, this includes T_(CQM2) and runs until T_(FCS)at FCS 208. Depending upon the positioning of DTIM IE 206 within thebeacon 201 and T_(C), zones 210, 211 and 212 may overlap to some degree,such as by one or more IEs. In the embodiments discussed herein, PTThzone 210 and TFTh zone 211 overlap by at least DTIM IE 206 and may beused to determine the validity window.

The above discussion relates to the reception of a beacon frame 201 byclient device 103A-103F. As will be appreciated, the techniques of thisdisclosure may be extended to other types of frames, such as othermanagement frames, control frames or data frames. Although such framesmay not include a DTIM IE 206, other suitable intermediate IEs may beused in a similar manner. In particular, it will be appreciated that avalidity window may be established with regard to any desired IE locatedat an intermediate location of the frame so that the information may beverified prior to receiving the entire frame. As such, reception of theframe may be terminated after receiving the desired IE to provideincreased power efficiency as compared to receiving the entire frame.

Next, a channel quality threshold (CQTh) may be empirically set to avalue which reflects a given percentage of confidence that FCSverification will (or would) succeed, referred to herein as the FCSconfidence level (FCL) and can be viewed as the percentage chance thatthe information received to this point has been decoded correctly. Aswill be appreciated, the FCL may be adjusted as desired depending uponperformance goals, design constraints and the like. In a currentlypreferred embodiment, the FCL may be in the range of approximately 80 to90%. As will be described, a CQM greater than the CQTh allows thedetermination of a corresponding validity window.

For example, when the CQM is the SNR, a suitable CQTh may correspond toa value that is approximately 2 dB greater than the minimum SNRassociated with the Modulation/Coding Set (MCS) used to transmit theframe. Similarly, when the CQM is the Rx-EVM, a suitable CQTh may beestablished in relation to the minimum required by the MCS being used.

In another example, the Viterbi confidence metrics may be observed overa suitable traceback length, such as 10 orthogonal frequency divisionmodulation (OFDM) symbols or approximately 100-128 bits, and compared toa CQTh corresponding to the desired FCL. In one aspect, a Viterbiconfidence metric may be determined by selecting a minimum path metricsuch that it exceeds a sum of the absolute values of all soft Viterbivalues corresponding the current frame that have been output. The sum ofsoft Viterbi values may be scaled by a suitable threshold factor, suchas a 6-bit number and performing a right-shift bit operation to generatea suitable range of 0 to 63/256. For some embodiments, when the receivedframe is not in the IEEE 802.11n protocol but includes a legacy signalfield (L-SIG), the state 0 metric at the end of L-SIG decoding may bechosen as the minimum path metric. In another aspect, the Viterbiconfidence metric may be determined by the difference between the nextsmallest minimum path metric and the minimum path metric, such that thedifference is below a suitable threshold.

In yet another example, for systems employing an IEEE 802.11b protocol,a running Rx-EVM may be used given that the structure of the preamblemay not allow use of the other CQMs described above. Further, using theconfidence metrics of the Viterbi output to augment the determinationbased on Rx-EVM may provide improved results.

The coherence time of the channel, T_(C), is also determined as known tothose of skill in the art. For example, based upon an IEEE TGn channel-Bcorrelation time profile, the coherence time varies depending upon therelative motion between the stations. In generally, greater relativemotion corresponds to shorter coherence time, such as 4.2 ms given arelative speed of 4.0 km/h, typical in IEEE 802.11X limited mobilityscenarios. The channel coherence time is usually reduced to fractions ofmilliseconds in vehicular conditions common in cellular communications,where system designers account for mobility in the 300 km/h range. Inone aspect, the coherence time applicable to IEEE TGn standard can bedetermined based the following equation:

$\begin{matrix}{T = {\frac{\sqrt{A}}{2\; \pi \; f_{d}} \cdot {\ln (2)}}} & (1)\end{matrix}$

in which T is the coherence time T_(C), f_(d) is the Doppler spread andA is a constant.

Relevant to the PTTh zone 210 referenced above, a preamble to DTIMthreshold, PTTh, is established corresponding to the period of timebetween the generation of the CQM at T_(CQM1) and the DTIM IE 206 atT_(TIM). This threshold should be set to period of time during which itcan reasonably be expected that the channel will be sufficiently uniformand stable to accurately transfer information from access point 101 toclient device 103A-103F. Depending upon the number of IEs 205 includedin beacon 201, Δ_(PT) may exceed PTTh. Relevant to the TFTh zone 211, aDTIM IE 206 to T_(CQM2) threshold, TFTh, is set to a period of timeduring which it can be expected that the channel is sufficientlycoherent to allow correct decoding of the beacon information. If FCS 208is beyond the TFTh zone, there is a finite probability that verificationmay fail due to channel impairments, introduced in the error zone 212.Similarly, depending upon the number of IEs 207 included in beacon 201,Δ_(TF) may exceed TFTh.

A further parameter associated with the channel assessment techniques ofthis disclosure is an N-update value that corresponds to the number ofIEs that may be trusted within the PTTh zone 210 and TFTh zone 211 basedupon the relationship between CQM taken at T_(CQM1) and CQTh. In oneembodiment, a value for N-update is pre-established based on testing orin any other suitable manner and may be implemented any time CQTh ismet. In a further aspect, N-update may be dynamically revised based uponthe degree to which the first CQM, computed at T_(CQM1), exceeds CQTh.Accordingly, PTTh zone 210 and TFTh zone 211, as optionally modified bythe N-update value, may be considered a validity window for the purposesof this disclosure

As discussed above, the terminal CQM, measured at T_(CQM2), may becomputed to evaluate the degree to which the channel is changing.Accordingly, a Δ_(CQTh) value is set that corresponds to the maximaldifference between the CQMs taken at T_(CQM1) and T_(CQM2) to reasonablyensure the channel has not degraded to a degree that would preventcorrect decoding of the data transmitted by access point 101. IEEE802.11X receivers, including client devices 103A-103F, may be configuredto supply values, such as SNR, SINR and RSSI, used to compute the CQMduring the preamble from the short or long training symbols and from thepilot error vector magnitude (EVM.) Since the CQM computed at T_(CQM2)occurs outside the preamble, training symbols are not available for thecomputation and conventional wireless receivers may not be configured toperform some types of CQM measurements subsequent to the preamble.Accordingly, in one embodiment of this disclosure, pilot symbolsspecifically from TFTh zone 211 may be analyzed to determine the zonalSNR. In another embodiment the CQM, computed at T_(CQM1), may becontinuously adjusted from the Pilot EVM at each OFDM symbol leading upto the T_(CQM2) instant. While advanced signal processing techniques canbe applied for this continuous adjustment, a fairly simple, butsufficiently reasonable, algorithm would be to store the first channelnoise contribution at T_(CQM1), excluding the Noise Figure of the analog(RF) front-end, followed by per-symbol Pilot EVM evaluation andadjusting, adding or subtracting, the first channel noise by an exact orfractional amount the Pilot EVM has differed, leading up to the T_(CQM2)zone. As desired, any other suitable technique may be employed todetermine CQM at T_(CQM2).

Accordingly, the above parameters including the CQMs determined atdifferent times during the reception of a frame, the CQTh, the durationmetrics, the coherence zones, and/or the N-update values may be employedto determine a validity window within a frame being received such thatIEs or other information inside the window may be verified as beingcorrectly received at a corresponding FCL level and utilized even if thereception of the frame is terminated prematurely or the FCS check fails.In a first aspect, the validity window may be determined by assessingwhether a first duration metric corresponding to the time period betweenthe preamble and reception of intermediate IE is within the coherencetime expected for the channel. If the initial CQM exceeds an appropriateCQTh, the validity window may be defined as spanning the period betweenthe reception of the preamble and the reception of intermediate IEcorresponding to PTTh Zone 210, with a degree of confidence FCL relatedto the CQM. In a second aspect, determining that an intermediate CQMexceeds a corresponding CQTh may establish a validity windowencompassing a given intermediate IE. As discussed above, if the CQMcomprises the confidence metrics from the output of the Viterbi decoderor a running Rx-EVM, greater than the minimum required for that givenMCS, a CQM value exceeding the appropriate CQTh may indicate the channelis valid within range of symbols upstream and downstream of the time theCQM is determined. In one embodiment, a validity window may not becontinuously updated and the last determined CQM may be consideredapplicable for at least a period of time corresponding to the T_(C) ofthe channel.

Turning now to FIG. 3, a block diagram illustrates one example of awireless client device 103A-103F configured to communicate with anaccess point 101 consistent with the techniques described herein. Asshown in FIG. 3, access point 101 includes an Internet module 348, apower source 346, a processor 344, a memory 345, a data processingmodule 340, and a communications module (COM module) 342.

Memory 345 may include any component of access point 101 configured tostore data. For example, memory 345 may include a temporary memory, suchas one or more random access memory (RAM) components or other short-termdata storage component. According to other examples, memory 345 mayinclude one or more long-term storage components, such as a magnetichard drive, FLASH memory component, or other long term data storagecomponent.

Processor 344 may comprise one or more components of access point 101configured to execute instructions (e.g., instructions stored in memory345). Processor 344 may comprise, for example, a general purposecomputing component (e.g., a central processing unit (CPU), graphicsprocessing unit (GPU)), or other computing component configured toexecute instructions stored in memory 345 to operate according to thetechniques described herein. For example, functionality described withrespect to one or more of data processing module 340, COM module 342,and Internet module 348 may at least in part, comprise instructionsexecutable by processor 344 to cause processor 344 to operateconsistently with the techniques described herein. In other examples,functionality of one or more components of access point 101 describedherein may be implemented using one or more components specificallyconfigured to perform the described functionality. For example, one ormore components of access point 101 described herein may comprise one ormore components (e.g., application specific integrated circuit (ASIC),field programmable gate array (FPGA), discrete logic component)specifically configured or arranged to operate according to thetechniques described herein.

Internet module 348 may be configured to enable access point 101 tocommunicate via a larger network, such as the Internet. For example, asdescribed above, Internet module 348 may include one or more hardware orsoftware components configured to enable access point 101 to communicatewith computing devices via the Internet using a wired communicationsprotocol. For example, Internet module 348 may include a modem internalor external to access point 101, such as a cable, DSL, T1, or T3 modemconfigured to enable access point 101 to communicate via a network, suchas the Internet. According to other examples, Internet module 348 mayenable access point 101 to communicate with a network, such as theInternet, wirelessly. For example, Internet module 348 may comprise oneor more hardware or software components of access point 101 configuredto enable access point to communicate wirelessly (e.g., via a 3G or 4Gcellular network) via a network, such as the Internet.

As depicted in FIG. 3, access point 101 includes a power source 346.Power source 346 may comprise any source of energy configured to powerone or more components of access point 101 for operation. For example,power source 346 may comprise an electrical coupling to an externalpower source (e.g., a wall outlet). According to other examples, forexample where access point 101 is a mobile device configured to operateas a wireless access point, power source 346 may comprise an externalpower source as described above and/or a battery or other form of energystorage component internal to or external from access point 101.

FIG. 3 also illustrates that access point 101 includes a data processingmodule (DPM) 340 and a communication (COM) module 342. Generallyspeaking, DPM 340 may receive data from another computing device viaInternet module 348, and process data received from Internet module 348.DPM 340 may send data to client device 103A-103F via COM module 342. Forexample, DPM 340 may arrange data received via Internet module 348 inone or more frames to be sent to client device 103A-103F wirelessly viaCOM module 342. According to one specific example, DPM 340 may arrangereceived data in one or more frames according to one or more of the IEEE802.11X standards for WI-FI wireless communications. In some examples,DPM 340 may also be configured to receive and process data received fromclient device 103A-103F via COM module 342. For example, DPM 340 mayprocess one or more frames of data or instructions from client device103A-103F, and send data or instructions from the one or more receivedframes to another computing device, e.g., via Internet module 348.

In some examples, DPM 340 may store received data in memory 345, priorto sending the received data to client device 103A-103F in the form ofone or more frames of data. In some examples, DPM 340 may communicateone or more frames of data stored in memory 345 to client device103A-103F, after access point 101 has sent client device 103A-103F abeacon 201 that includes a DTIM IE 206 that indicates the one or moreframes of data stored in memory 345 are forthcoming from access point101.

As shown in FIG. 3, client device 103A-103F includes a communicationsmodule (COM module) 352, a processor 354, a memory 355, a dataprocessing module (DPM) 350, a power source 356, and a power mode module(PMM) 357.

Memory 355 may include any component of client device 103A-103Fconfigured to store data. For example, memory 355 may include atemporary memory, such one or more random access memory (RAM) componentsor one or more other short term data storage components. According toother examples, memory 355 may include one or more long term storagecomponents, such as one or more magnetic hard drives, FLASH memorycomponents, or one or more other long-term data storage components.

Processor 354 may comprise one or more components of client device103A-103F configured to execute instructions (e.g., instructions storedin memory 355). Processor 354 may comprise, for example, a generalpurpose computing component (e.g., a central processing unit (CPU),graphics processing unit (GPU)), or other computing component configuredto execute instructions stored in memory 355 to cause client device103A-103F to operate as described herein. For example, functionalitydescribed with respect to one or more of data processing module 350,DTIM module 358, channel assessment module 359, PMM 357, and/or COMmodule 352 may at least in part, comprise instructions executable byprocessor 354 to cause processor 354 to operate cause client device103A-103F to operate consistent with the techniques described herein. Inother examples, one of more modules of access point 101 described hereinmay also or instead be implemented, at least in part, using one or morecomponents specifically configured to perform the functionalitydescribed herein. For example, one or more modules of client device103A-103F described herein may comprise one or more components (e.g.,application specific integrated circuit (ASIC), field programmable gatearray (FPGA), discrete logic component) specifically configured orarranged to operate according to the techniques described herein. Thevarious modules of client device 103A-103F described herein may beimplemented using any combination of hardware, software, firmware,discrete logic components.

As one specific example, COM module 352 may include instructionsexecutable by processor 354 to cause client device 103A-103F tocommunicate with access point 101 and/or one or more circuitsspecifically configured to cause client device 103A-103F to communicatewith access point 101. For example, COM module 352 may include one ormore components (e.g., a WI-FI integrated circuit (WI-FI IC) configuredto enable client device 103A-103F to communicate using one or more ofthe IEEE 802.11X standards for WI-FI communication.

Power source 356 may include any component of client device 103A-103Fconfigured to store or access power to operate one or more components ofclient device 103A-103F, such as COM module 352, DPM 350, PMM 357, orother component of client device 103A-103F. In some examples, powersource 356 of client device 103A-103F may include limited power source,such as a battery. In other examples, power source 356 may comprise anexternal power source, such as an external coupling to a wall outlet, ora battery external to client device 103A-103F. In some examples, whereclient device 103A-103F uses a limited power source such as an internalbattery, it may be desirable to minimize power consumption of clientdevice 103A-103F, in order to increase a battery life of client device103A-103F.

To reduce power consumption of client device 103A-103F, PMM 357 depictedin FIG. 3 may operate client device 103A-103F in different modes ofoperation. For example, PMM 357 may cause client device 103A-103F tooperate in an active mode, or a low power consumption mode to reducepower consumption of client device 103A-103F. According to such a lowpower consumption mode, one or more components of client device103A-103F may be turned off, and/or operated at a slower rate and/orwith a reduced power supply (e.g., a reduce supply voltage and/orcurrent) in comparison to an active mode of operation. For example, inan active mode of client device 103A-103F, PMM 357 may cause COM module352 (e.g., a WI-FI integrated circuit (IC) of client device 103A-103F tobe turned on (e.g., connected to power source 356) such that clientdevice 103A-103F may communicate with access point 101. According tothis example, in a low power consumption mode, PMM 357 may turn off COMmodule 352, such that COM module 352 may consume little or no power frompower source 356. For example, according to the low power consumptionmodule, PMM 357 may disconnect COM module 352 from power source 356,such that COM module 352 may not consume any power. According to otherexamples, according to a low power consumption mode, PMM 357 may causeDPM 350 not to process data received by access point 101.

As shown in FIG. 3, DPM 350 includes a DTIM module 358. According to thetechniques described herein, DPM 350 may receive a header 204 of abeacon 201 as depicted in FIG. 2. DPM 350 may then begin receiving IEs205. DTIM module 358 may determine that DTIM IE 206 comprises the DTIMIE. For example, DTIM module 358 may determine that DTIM IE 206 is theDTIM IE based on information of header 204, or information in a headerof DTIM IE 206. DTIM module 358 may further determine, based on DTIM IE206, whether one or more frames of data are forthcoming from accesspoint 101. If the DTM 206 indicates that one or more frames of data areforthcoming from access point 101, client device 103A-103F may continueto operate in an active mode, to receive the forthcoming frames of datafollowing DTIM IE 206, such as IEs 207. Otherwise, if one or more framesof data are not forthcoming from access point 101, DTIM module 358 maycause client device 103A-103F to be operated in a low power consumptionmode (e.g., via PMM 357). Accordingly, client device 103A-103F may notreceive data segments following DTIM IE 206.

As also shown in FIG. 3, client device 103A-103F also preferablyincludes a channel assessment module 359. As described above, one ormore parameters including the initial CQM at T_(CQM1), one or moreintermediate CQMs, the terminal CQM at T_(CQM2), PTTh, TFTh, N-update,T_(C), Δ_(PTΔPT), Δ_(TF) and Δ_(CQTh) parameters may be used in variousmanners to enable client device 103A-103F to assess channel conditionsso that the validity of the DTIM and other IEs can be gaugedindependently of FCS verification. Channel assessment module 359 ispreferably configured with the set parameters and is also preferablyconfigured to receive channel quality information from the PHY layer inthe form of SNR, SNIR, RSSI, Rx-EVM, confidence metrics from the Viterbioutput or other suitable measure of signal quality. Channel assessmentmodule 359 is also preferably configured to perform the abovecomparisons with the thresholds to establish the FCL % confidence of theDTIM and other IEs. Client device 103A-103F also preferably includestiming estimation module 360, which is configured to perform thecoarse-adjustment and fine-adjustment estimations regarding the expectedTSF range described above. For example, timing estimation module 360preferably samples per-frame (PPDU) drift information, triggered at eachbase-interval. In one embodiment, such fine-time stamps may be obtainedby any suitable means generally known in state of the art, such as fromSTF and/or LTF processing.

Although these channel awareness parameters and the techniques of thisdisclosure may utilized during the reception of any suitable frame,within the context of an EBT scheme, it will be appreciated that certainscenarios may involve a client device 103A-103F. In a first example,client device 103A-103F receives beacon 201 in which DTIM IE 206 is notset. In a second example, client device 103A-103F receives beacon 201 inwhich DTIM IE 206 is set. These two scenarios are discussed in detailbelow.

In the first noted example of an EBT implementation according to theprinciples of this disclosure, client device 103A-103F may receiveand/or process a validity window such as PTTh zone 210 of beacon 201followed by DTIM IE 206. Under this example, client device 103A-103Fdetermines, based on the DTIM IE 206, that frames of data are notforthcoming from access point 101. Since DTIM IE 206 is not set, clientdevice 103A-103F may implement EBT, entering a low power mode and notreceiving any information from portions of beacon 201 following DTIM IE206. As a result, client device 103A-103F may not receive FCS 208 andwill be unable to perform the FCS check to validate data of beacon 201.

As discussed above, the validity window may include informationregarding important system parameters, including the TSF. This IE mayindicate, to a client device 103A-103F, when the client device shouldawake from a low power mode of operation to receive at least one furtherbeacon from access point 101. For example, the TSF may indicate acounter value, such as a 64-bit timer counter with micro secondresolution. Client device 103A-103F may use the TSF to synchronize a TSFtimer counter internal to client device 103A-103F with a TSF timercounter of access point 101. In some examples, client device 103A-103Fmay use the TSF to synchronize operation with access point 101, forexample, to compensate for clock drift between internal clock references(e.g., crystal oscillators) of the client device 103A-103F and theaccess point 101. In yet other examples, the client device may use theTSF to implement other technologies depending upon accurate clocksynchronization between access point 101 and client device 103A-103,such as positioning functions. Additional important system parameterscommunicated during the validity window may include the CSA IE andothers.

One of skill in the art will appreciate that it may be desirable toupdate important system parameters such as the above only when there isreasonable confidence the information received from beacon 201 is valid.When EBT operates to abort beacon reception prematurely, FCS 208 is notreceived and its validation function is not available. Under situationswhere access point 101 does not have forthcoming data for a period oftime, DTIM FE 206 is not set, FCS 208 is not received, and the TSF orother system parameters may not be updated under conventional EBTtechniques.

Accordingly, one aspect of this disclosure is to determine a validitywindow based on channel awareness that is independent from FCS so thatTSF and other system parameters may be updated even during periods whenthe access point 101 has no pending data for client device 103A-103F. Byapplying the channel awareness parameters discussed above, a very goodindication of the data integrity in the validity window may bedetermined. For example, a validity window established in relation to anintermediate IE may be used to provide a corresponding FCL forinformation received within the window upstream and downstream from theintermediate CQM determination. Likewise, the channel parameters CQM andCQTh, coupled with duration (PTTh) and coherence parameters (TC) may beused to provide a high degree of confidence in data segments receivedprior to an intermediate IE, such as DTIM IE 206, provided Δ_(PT) isless than or equal to the lesser of PTTh or T_(C) for a validity windowcorresponding to PTTh zone 210. If the Δ_(PT) satisfies this condition,CQM is compared to CQTh. As will be appreciated, the CQM at a given timeis available from the physical layer (PHY) of client device 103A-103F.Accordingly, if the signal quality meets the threshold, data within thePTTh zone 210 can be treated as valid. Thus, when Δ_(PT) is less thanthe PTTh, it can be seen that IEs 205 received during PTTh zone 210 aretransmitted during a period of time when the channel conditions areunlikely to have changed. Similarly, when Δ_(PT) is less than T_(C),such IEs 205 are transmitted during a period less than the coherencetime. In both situations, the channel assessment indicates that theinformation received prior to DTIM IE 206 has the established FCL ofbeing valid as the signal quality was adequate at T_(CQM1).

Under the above conditions, the data received by client device 103A-103Fprior to the DTIM IE 206 can be identified as correctly decoded datawith FCL % confidence. As desired, having this degree of confidenceallows the TSF counter and other parameters to be updated. Further, theN-update value may be revised to reflect the validity window or PTThthreshold. In some embodiments, it may be also be desirable to perform atertiary check before updating the TSF.

For example, the received value can be reviewed to determine whether thecounter is within an expected range, such as by ensuring the interval iscommensurate with the beacon transmission interval. The expected rangeis a fuzzy function of the beacon interval (BI). As an example, if theBI is 100 ms, the beacon duration is encoded as 100 TU (transmissionunits) in the TSF. The expected range of the counter is recommended tobe within a defined percentage, such as approximately 20%, of the beaconduration, i.e., {80, 120} TUs, assuming the Listen Interval (LI) is 1.For a LI of N, the expected range would be N*{80, 120} TUs. As will beappreciated, this parameter of the algorithm may be modified at desired.

In an alternative embodiment, a more specific bound of the expected TSFrange may be employed at a slightly higher hardware and/or softwareprocessing cost. By using a priori information of clock drifts, obtainedfrom a fine timing estimation procedure for example, this approach takesadvantage of the accuracy of the crystal oscillators used on the accesspoint and on the client device. The accuracy is typically quantified bya Parts-Per-Million (ppm) count and reflects how many clock cycles theclock is expected to drift over a period of time, if left uncorrected.In one example, the Beacon Interval may be 100 ms and the ListenInterval may be 10, which is typical when 802.1X is deployed inpower-aware mobile devices, e.g., tablets, cell phones etc. As such, thebase-interval, or the interval of inactivity on the client side, may begiven as (LI*BI) ms. In this example, then, the base-interval is 1000ms, or 1 second. Given a clock accuracy of 1000 ppm, which isrepresentative for systems using an internal local oscillator to clockduring inactive periods, the clock may be expected to drift by 1 msduring the inactivity period, requiring an early wake-up on the clientdevice and results in a waste of power. While the accuracy of the clocksis generally a fixed quantity on both sides, it is also subject to mildfluctuations due to temperature changes.

Accordingly, in these noted embodiments, the client device preferablyrecords the clock drift over several consecutive base-intervals (BI*LI),with any EBT procedures disabled, for a configurable amount of time,parameterized by N_(training). The outcome of this training is an amountthat quantifies the expected clock drift on the access point for theduration of the base interval, i.e., drift-per-base-interval (DPBI). Inother words, DPBI indicates how much of a drift the access point mayhave encountered and directly corresponds to an expected range ofvariability for the TSF. Further, a complementary DPBI calibration maybe done periodically on the client side, subject to significant pre-settemperature variations, the threshold of which may be left as a choiceto the system designer. This DPBI re-calibration helps resolveuncertainty on the client side and serves as an input to the earlywake-up logic as well. Using such estimations of DPBI, a stricter boundon the expected TSF range may be obtained.

As described above, channel metrics may be used to initially improveconfidence in un-verified IEs. In turn, these tertiary TSF checks helpensure that the un-verified TSF is at least bounded by DPBI, from theotherwise exact value. When applying other power saving techniques likeskipping multiple, say M, base-intervals, known as telescopic DTIM instate of art, DPBI characterization may be used to extend the expectedTSF range to M*DPBI. As will be appreciated the type of tertiary checkand the parameters used may be adapted to obtain a desired level ofperformance.

Preferably, the DPBI re-calibration may involve a coarse-grained andfine-grained estimation. For example, the coarse-grained adjustment maybe triggered based on temperature fluctuations on the client deviceabove a pre-set threshold or for cases like telescopic DTIM where thedevice has remained uncorrected for a several multiple ofbase-intervals. The fine-grained adjustment, on the other hand, may beconfigured to occur at each base-interval, when the client devicereceives a PPDU frame. A fine timing estimate, in terms of a few clockcycles, then may be provided from the physical layer processing, such asbaseband processing, and suitable analysis of STF and LTF symbols, tocorrect the DPBI at each interval. The coarse grained DPBI adjustmentmay resolve the local (client side) clock uncertainty and may notnecessarily improve the TSF range. As such, the coarse estimate may beused to minimize early wake ups of the client device. The fine grainedadjustment, on the other hand, may resolve uncertainty on the accesspoint side and therefore impacts the TSF range directly.

As described above, the validity window may be employed to gainconfidence that IEs received during that period are correct absent atypical verification process. Correspondingly, when the above parametersfail to meet the criteria, either when Δ_(PT) is greater than PTTh orDTIM message 220 or when CQM does not exceed CQTh, it may be concludedthat a validity window does not exist and that the data segmentsreceived prior to DTIM IE 206 are not valid. Such data segments may beidentified as incorrectly decoded data with a degree of confidenceassociated with the FCL. Since there is insufficient reliability forsuch data, TSF and other system parameters are preferably not updatedand the normal EBT procedure may be followed to put client device103A-103F in low power mode when DTIM IE 206 is not set and discard thedata from beacon 201.

Turning to the second noted example of EBT operation, situations inwhich DTIM IE 206 is set are encountered. In this scenario, clientdevice 103A-103F may continue to receive beacon 201 through terminationat FCS 208. If FCS passes, all the data within beacon 201 may be treatedas valid. However, even if FCS fails, the data transmitted around DTIMIE 206 may have been received correctly. By employing the channelassessment parameters discussed above, the techniques of this disclosureare used to make a determination of confidence allow for the validity ofdata transmitted during the PTTh zone 210 and TFTh zone 211.Correspondingly, when sufficient confidence exists, this data may betreated as valid. This will result in a performance improvement ascompared to situations when valid data is discarded due to FCS failure.

Specifically, when DTIM IE 206 is set and FCS fails, the error may haveoccurred either in the DTIM or in a different portion of beacon 201. Aswill be appreciated from the following discussion, the channelparameters CQM and CQTh in conjunction with distance (TFTh) andcoherence (T_(C)) parameters may be employed to provide a strongindication of the data integrity around DTIM IE 206 and to help diagnosethe FCS failure.

A first stage of the analysis is directed to the CQM and Δ_(PT)parameters. If CQM exceeds CQTh, good channel conditions may bedetermined to exist during receipt of the preamble. Likewise, if Δ_(PT)is less than the lesser of PTTh or T_(C), the period of time between theCQM determination and DTIM IE 206 is sufficiently short to determinethat the channel conditions at T_(CQM1) will not have changedsubstantially. When these two conditions are met, it is preferable todetermine that the DTIM IE 206 was correctly decoded, with a confidenceof FCL %. Also preferably, a tertiary check may be performed toestablish the cause for FCS failure as discussed below

Once there is reasonable confidence that DTIM IE 206 was correctlyreceived, the channel assessment parameters may be employed to diagnoseat what stage an error occurred, leading to the FCS failure.Specifically, a second stage of the analysis is directed to Δ_(TF) andΔ_(CQTh). Δ_(TF) being greater than the lesser of TFTh or T_(C)indicates that the length of beacon, particularly due to the number ofIEs 207, is sufficiently long that it is likely the channel degradedafter receipt of DTIM IE 206, somewhere inside Error Zone 212.Alternatively, the difference between the CQM determined during thepreamble at T_(CQM1), and the CQM determined after the receipt of DTIMIE 206 at T_(CQM2), is compared to Δ_(CQTh). When the difference betweenthe two CQMs exceeds Δ_(CQTh), it indicates a significant degradation inchannel quality. If either of these conditions is met, it is likely asudden degradation of the channel condition occurred after reception ofDTIM IE 206, as a result, for example, of symbol erasures not affectingthe DTIM IE.

Therefore, if both the first and second aspects of the analysis agree,client device 103A-103F preferably determines DTIM IE 206 was setcorrectly. In turn, this allows client device 103A-103F to correctlyrespond to access point 101, even though FCS failed. For example, whenDTIM IE 206 indicates that TIM is set, client device 103A-103F respondsto access point 101 with a PS-POLL transmission or when DTIM IE 206indicates DTIM is set, the client device prepares to receive broadcastdata from access point 101. In a further aspect, the fulfillment ofthese aspects also allows client device 103A-103F to have a confidenceof FCL % that data received prior to DTIM IE 206 is valid, allowingsystem parameters such as TSF and CSA to be updated. If either aspect ofthe analysis fails, client device 103A-103F may not determine that DTIMIE 206 was correctly decoded and is preferably configured to revert tolegacy error handling mechanisms.

Suitable exemplary algorithms for performing these determinations withrespect to the duration metrics are discussed below with respect toFIGS. 4 and 5. FIG. 4 is a flow diagram that illustrates one example ofa method of operating a client device consistent with the techniques ofthis disclosure. The method depicted in FIG. 4 is described with respectto client device 103A-103F depicted in FIG. 3, however other devices mayalso be used. As shown in FIG. 4, a suitable algorithm for assessingchannel conditions to allow the validity of IEs to be determinedindependently of conventional FCS verification. DPM 350 of client device103A-103F begins reception of beacon 201 by processing PLCP preamble202, obtaining CQM1 from the PHY layer at T_(CQM1) in step 401. Next,DPM 350 begins reception of the PDSU frame, including header 204followed by IEs 205 and then finally DTIM IE 206 at T_(TIM) in step 402.In step 403, channel assessment module 359 determines Δ_(PT) fromT_(CQM1) and T_(TIM). In step 404, if DTIM IE 206 is not set, thealgorithm continues to step 405 to implement the EBT feature, such thatPMM 357 places client device 103A-103F in low power mode, abortingreception of beacon 201. Alternatively, if DTIM IE 206 is set, thealgorithm goes to step 501, discussed below with respect to FIG. 5.

Even though EBT aborts reception of beacon 201, IEs 205 have alreadybeen received by DPM 350 and may be used if the validity of the data isdetermined to a sufficient level of confidence without the reception ofFCS 208. To this end, channel assessment module 359 compares Δ_(PT) tothe lesser of PTTh or T_(C) in step 406. If Δ_(PT) is less than eitherof these parameters, the algorithm continues to step 407 in whichchannel assessment module 359 compares CQM1 to CQTh. If the signalquality meets the threshold, data within the PTTh zone 210 may bedetermined valid with a confidence of FCL %. Preferably, a tertiarycheck is performed in step 408 to ascertain whether the TSF valuereceived from IEs 205 is within an expected range.

In one embodiment, the interval may be compared with the beacontransmission interval such that the received TSF is within a definedrange, such as within approximately 20%, of the exact expected TSF. Inanother preferred embodiment, the expected range may be more tightlybound by combining with clock accuracies (ppm count) and a prioricharacterization of the DPBI as described above. The drift refers toclock-drift over a period of time, subject to clock ppm count, and baseinterval refers to the fundamental sleep interval of the client device,given by (BI*LI)ms. Preferably, a periodic coarse-adjustment to the DPBImay be based upon temperature fluctuations around pre-set thresholds.Also preferably, a fine-adjustment may be triggered at eachbase-interval by taking per-frame (PPDU) drift information. Suchfine-time stamps can be obtained by any suitable means generally knownin state of the art, such as from STF and/or LTF processing. Asdescribed above, timing estimation module 360 is preferably configuredto provide these estimations.

With a successful check in step 408, the algorithm continues to step409, in which channel assessment module 359 authorizes system parameterssuch as TSF and CSA to be updated using information from IEs 205. Asdescribed above, an established N-update value may be implemented whenthe CQTh is met. Alternatively, the N-update value may be dynamicallyupdated based on the relationship of CQM at T_(CQM1) to CQTh, when thefirst CQM is more than CQTh by a pre-determined margin. In oneembodiment, such a margin to number of IEs to update can be pre-computedand stored in a look-up table within the DTIM module 358. The N-updatevalue corresponds to the number of IEs in PTTh zone 210 and TFTh zone211 that may be considered valid. If Δ_(PT) is not less than PTTh orT_(C) in the comparison of step 405, or if the signal quality is notsufficient as determined in step 407, the algorithm terminates at step410 and data from PTTh zone 210 is preferably discarded.

Turning now to FIG. 5, a flow diagram that illustrates another exampleof a method of operating a client device consistent with the techniquesof this disclosure is depicted. As indicated above with regard to step404, if DTIM is set, DPM 350 continues to receive beacon 201 followingDTIM IE 206, including IEs 207 and terminating with FCS 208 at T_(FCS)in step 501. Channel assessment module 359 also determines Δ_(TF) fromT_(TIM) and T_(FCS). Concurrently, channel assessment module 359 setsT_(CQM2) based upon TFTh and computes CQM2 at T_(CQM2) from informationfrom the PHY layer of client device 103A-103F in step 502. Next, thedata from FCS 208 is used to determine the validity of beacon 201 instep 503. If FCS passes, the algorithm continues to step 504 and alldata from beacon 201 is treated as valid and client device 103A-103Foperates conventionally. Alternatively, if FCS fails, channel assessmentmodule 359 determines whether CQM1 at T_(CQM1) exceeds CQTh in step 505and then determines whether Δ_(PT) is less than the lesser of PTTh orT_(C) in step 506. If either condition is not met in step 505 or 506,the algorithm exits to step 508, preferably discarding the data frombeacon 201 and executing legacy error handling mechanisms.

If both conditions from steps 505 and 506 are met, the channelassessment parameters are preferably employed to diagnose the stage atwhich errors receiving beacon 201 occurred leading to the FCS failure.Accordingly, in step 509 channel assessment module 359 determineswhether Δ_(TF) is greater than the lesser of TFTh or T_(C) to assess thelength of beacon 201 following DTIM IE 206. For example, if Δ_(TF) isgreater than TFTh, this indicates there is an Error Zone 212 as thechannel may reasonably be assumed to have varied sufficiently to causeincorrect data decoding. The algorithm then continues to step 510, todetermine the degree to which channel conditions have changed byT_(CQM2) such that CQM2 is compared to CQM1 to ascertain whether channelconditions have changed in fact. If the difference between CQM2 and CQM1meets the Δ_(CQTh), it may be determined that channel conditions havechanged sufficiently to account for the FCS failure within the errorzone 212.

Thus, if Δ_(TF) is not sufficiently long as determined from step 509 orif the difference in CQM is less than Δ_(CQTh), there may beinsufficient support to conclude that the FCS failure was a result ofchanging channel conditions. Without an indication of the reason for FCSfailure, the algorithm preferably exits to step 508 and the data isdiscarded. Otherwise, it may be determined that the FCS failure may beattributed to either the length of beacon 201 or the observed change insignal conditions. Thus, if both conditions of steps 509 and 510 aremet, the algorithm proceeds to step 511 and channel assessment module359 preferably validates DTIM IE 206 and operates client device103A-103F accordingly, such as by allowing client device 103A-103F tocorrectly respond to access point 101 with a PS-POLL transmission or bypreparing to receive broadcast data as warranted.

Further, under these conditions channel assessment module 359 may alsopreferably determine that data segments received in IEs 205 prior toDTIM IE 206 are also valid, allowing system parameters such as TSF andCSA to be updated subject to the algorithm described above regardingFIG. 4.

While the examples discussed above in relation to FIGS. 4 and 5 aredirected to client device 103A-103F receiving beacon frame 201 andoptionally implementing an EBT scheme, FIG. 6 depicts a more generalizedapplication of the techniques of this disclosure in the context of usingthe channel awareness parameters to determine a validity window withrespect to an intermediate IE within any suitable frame. Beginning withstep 601, DPM 350 of client device 103A-103F starts reception of a frameby processing the PLCP preamble followed by the body of the PDSU frame.For the purposes of this disclosure, the portion of the PDSU framefollowing the header may be considered to comprise a sequence of IEs. Instep 602, channel assessment module 359 determines an intermediate CQMat time T_(i) and compares the determined CQM to an appropriate CQTh instep 603. If the intermediate CQM is greater than or equal to CQTh,channel assessment module 359 may establish a validity window inreference to T_(i), having a duration that depends at least in part onthe T_(c) of the channel in step 604. However, if CQM does not exceedCQTh, it may indicate that channel conditions are insufficient forproper reception and reception of the frame may be terminated in step605. In step 606, DPM 350 may process a given intermediate IE, IE_(n).As will be appreciated, the order of step 606 in relation to steps 602and 603 may be reversed if IE, is received before the intermediate CQMis determined or may occur substantially simultaneously.

Next, in step 607, channel assessment module 359 determines whetherIE_(n) falls with the validity window. If not, IE_(n) may be discardedin step 608. Otherwise, the algorithm may branch at step 609 dependingupon whether DPM 350 continues to receive the frame through the FCS. Ifnot, the algorithm may continue to step 610 and IE_(n) may be treated ascorrectly received with a corresponding FCL. Optionally, as indicated bythe path to step 605, reception of the frame may be terminated to savepower following verification of IE_(n). On the other hand, if the FCS isreceived, its validity is determined in step 611. The algorithm may alsoproceed to step 610 if the FCS is valid, as this provides furtherindication that IE_(n) was correctly received. However, if the FCS isnot valid, the algorithm proceeds to step 612 to diagnose the cause ofthe FCS failure. Following the procedures described above with regard toFIG. 5, if a suitable reason may be determined for the failure of theFCS, the algorithm still proceeds to step 610 and IE, may be utilized.If the cause of the FCS failure cannot be determined, the algorithm mayend with step 608 such that IE, may be treated as being incorrectlyreceived.

The suitability of the techniques of this disclosure may be seen withregard to experimental comparisons of a CQM based upon SNR to thevalidity of the received frame as represented by the cumulativedistribution function (CDF) as shown in FIGS. 7-10 for various SNRstaken under non line of sight (D-NLOS) conditions. The frames used forthese simulations are 100B packets so these results may be extended tothe reception of longer frames by performing CQM determinations of SNRat intervals corresponding to 100 bytes at the particular data ratebeing employed. In particular, FIG. 7 depicts results at an SNRaveraging 6 dB at 1 Mbps and an average packet error rate (PER) of 10%.Curve 701 represents the SNR-based CQM of error-free frames while curve702 represents the SNR-based CQM of erroneous frames. By employing aCQTh based on the SNR exceeding 2 dB, erroneous data would be validatedless than 0.1% of the time while about 25% of correct frames may bedesignated as erroneous. FIG. 8 depicts results at an SNR averaging 15dB at 1 Mbps and an average PER of 1%. Curve 801 represents theSNR-based CQM of error-free frames while curve 802 represents theSNR-based CQM of erroneous frames. By employing a CQTh based on the SNRexceeding 2 dB, erroneous data would be validated less than 0.1% of thetime while about 3% of correct frames may be designated as erroneous.FIG. 9 depicts results at an SNR averaging 28 dB at 65 Mbps and anaverage PER of 10%. Curve 901 represents the SNR-based CQM of error-freeframes while curve 902 represents the SNR-based CQM of erroneous frames.By employing a CQTh based on the SNR exceeding 2 dB, erroneous datawould be validated less than 0.1% of the time while about 65% of correctframes may be designated as erroneous. Finally, FIG. 10 depicts resultsat an SNR averaging 36 dB at 1 Mbps and an average PER of 0.5%. Curve1001 represents the SNR-based CQM of error-free frames while curve 1002represents the SNR-based CQM of erroneous frames. By employing a CQThbased on the SNR exceeding 2 dB, erroneous data would be validated lessthan 0.2% of the time while about 3% of correct frames may be designatedas erroneous.

Further examples demonstrate the suitability of this disclosure withregard to experimental comparisons of a CQM based upon a Viterbi errormetric derived from the minimum path metric as described above to PER asshown in FIGS. 11 and 12. In particular, FIG. 11 depicts results underaverage Gaussian white noise (AWGN) test conditions using a scalingthreshold of 0.9. Curve 1101 represents the PER of frames filtered bythe Viterbi error metric and curve 1102 represents the PER of unfilteredframes as reference. As indicated by the close relationship of the twocurves, filtering by the Viterbi error metric results in almost noperformance degradation. Nevertheless, the use of a threshold of 0.9provides detection of approximately 99% of all false positive frames inwhich there are errors in the received bits of the L-SIG, butconventional verification based on parity, rate and a check of thereserved bits indicates correct decoding. Similarly, FIG. 12 depictsresults under D-NLOS conditions and also employs a scaling thresholdfactor of 0.9. Curve 1201 represents the PER of frames filtered by theViterbi error metric and curve 1202 represents the PER of unfilteredframes as reference. Again, the close relationship of the two curvesindicates minimal performance degradation resulting from Viterbi errormetric filtering while the threshold provides detection of approximately93% of all false positive frames.

The techniques described herein may be implemented in hardware,software, firmware, or any combination thereof. Any features describedas modules or components may also be implemented together in anintegrated logic device or separately as discrete but interoperablelogic devices. If implemented in software, the techniques may berealized at least in part by a tangible computer-readable storage mediumcomprising instructions that, when executed, performs one or more of themethods described above. The tangible computer-readable data storagemedium may form part of a computer program product, which may includepackaging materials.

Described herein are presently preferred embodiments. However, oneskilled in the art that pertains to the present invention willunderstand that the principles of this disclosure can be extended easilywith appropriate modifications to other applications.

What is claimed is:
 1. A client device for communicating with a wirelessaccess point, wherein the client device comprises a data processingmodule configured to receive at least a portion of a frame transmittedby the access point to an intermediate location within the frame and achannel assessment module configured to determine a validity window withrespect to the intermediate location when at least one channel qualitymetric is greater than or equal to a given threshold, wherein dataprocessing module is configured to validate information received withinthe validity window.
 2. The client device of claim 1, wherein thechannel assessment module is configured to determine the validity windowby setting a range of symbols upstream and downstream of a period oftime when the channel quality metric is determined.
 3. The client deviceof claim 2, wherein the channel quality metric comprises confidencemetrics from the output of a Viterbi decoder.
 4. The client device ofclaim 1, wherein the channel assessment module is configured todetermine the validity window based upon a coherence time for a channelused to transmit the frame.
 5. The client device of claim 1, wherein thechannel quality metric comprises a receiver error vector magnitude. 6.The client device of claim 1, wherein the channel quality metric isbased upon signal strength of the frame.
 7. The client device of claim1, wherein the given threshold is based upon a modulation coding setused for the transmitted frame.
 8. The client device of claim 1, whereinthe client device is configured to update system parameters based uponthe information received within the validity window.
 9. The clientdevice of claim 1, wherein the client device is configured to terminatereception of the frame when the channel quality metric does not exceedthe given threshold.
 10. The client device of claim 1, wherein thechannel assessment module is further configured to determine a pluralityof validity windows, such that each validity window is determined inreference to a channel quality metric determined at a different timeduring the frame.
 11. The client device of claim 1, wherein the frame isreceived though a verification field and the channel assessment moduleis further configured to diagnose a failure of the verification field onthe basis of a duration metric and a difference between a first channelquality metric measured during a preamble of the frame and a secondchannel quality metric measured during a time corresponding to theintermediate location, wherein the information within the validitywindow is validated when the failure diagnosis is attributable todeteriorating channel conditions.
 12. The client device of claim 1,wherein the information received within the validity window comprises aDTIM information element and wherein the client device if configured toterminate reception of the frame and enter a low power mode if the DTIMinformation element indicates there is no pending data at the accesspoint for the client device.
 13. The client device of claim 1, whereinthe channel assessment module is further configured to assign aconfidence level to the validity window based upon the channel qualitymetric and the given threshold.
 14. The client device of claim 1,wherein the channel assessment module is further configured to determinethe validity window by comparing a first duration metric correspondingto a time period between a preamble of the frame and the intermediatelocation to a coherence time and determining whether a first channelquality metric determined from the preamble exceeds a given threshold.15. The client device of claim 14, wherein the channel assessment moduleis further configured to determine the validity window by comparing asecond duration metric corresponding to a time period between theintermediate location and a verification field to a coherence time andcomparing the difference between the first channel quality metric and asecond channel quality metric to a channel quality difference threshold.16. A method for wireless communication with an access point,comprising: a) receiving at least a portion of a frame transmitted bythe access point to an intermediate location within the frame with aclient device; b) determining a channel quality metric; c) establishinga validity window when the channel quality metric is greater than orequal to a given threshold; and d) validating information from the framereceived within the validity window.
 17. The method of claim 16, whereinestablishing the validity window comprises setting a range of symbolsupstream and downstream of a period of time when the channel qualitymetric is determined.
 18. The method of claim 17, wherein determiningthe channel quality metric comprises obtaining confidence metrics fromthe output of a Viterbi decoder.
 19. The method of claim 16, whereinestablishing the validity window comprises using a range based upon acoherence time for a channel used to transmit the frame.
 20. The methodof claim 16, wherein determining the channel quality metric comprisesmeasuring a receiver error vector magnitude.
 21. The method of claim 16,wherein determining the channel quality metric comprises measuring asignal strength of the frame.
 22. The method of claim 16, wherein thegiven threshold is based upon a modulation coding set used for thetransmitted frame.
 23. The method of claim 16, further comprisingupdating system parameters of the client device based upon theinformation received within the validity window.
 24. The method of claim16, further comprising terminating reception of the frame when thechannel quality metric does not exceed the given threshold.
 25. Themethod of claim 16, further comprising determining a plurality ofchannel quality metrics at different times during the frame andestablishing a plurality of validity windows, each validity windowcorresponding to the plurality of channel quality metrics.
 26. Themethod of claim 16, wherein the frame is received though a verificationfield, further comprising diagnosing a failure of the verification fieldon the basis of a duration metric and a difference between a firstchannel quality metric measured during a preamble of the frame and asecond channel quality metric measured during a time corresponding tothe intermediate location, wherein the information within the validitywindow is validated when the failure diagnosis is attributable todeteriorating channel conditions.
 27. The method of claim 16, whereinthe validated information includes a DTIM information element, furthercomprising terminating reception of the frame and placing the clientdevice in a low power mode if the DTIM information element indicatesthere is no pending data at the access point for the client device. 28.The method of claim 16, further comprising assigning a confidence levelto the validity window based upon the channel quality metric and thegiven threshold.
 29. The method of claim 16, wherein establishing thevalidity window comprises comparing a first duration metriccorresponding to a time period between a preamble of the frame and theintermediate location to a coherence time and determining whether achannel quality metric determined from the preamble exceeds a giventhreshold.
 30. The method of claim 29, wherein establishing the validitywindow further comprises comparing a second duration metriccorresponding to a time period between the intermediate location and averification field to a coherence time and comparing the differencebetween the first channel quality metric and a second channel qualitymetric to a channel quality difference threshold.